The invention relates to the field of intravascular catheters, and more particularly to a balloon catheter or other catheter components, such as a guidewire enclosure and catheter tubing, that would benefit from the properties of the materials disclosed herein.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of an dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. The rate of expansion of the balloon for a given pressure is an important consideration in the design of the dilation catheter, as greater than anticipated expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed from the patient's artery.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion.
In the design of catheter balloons and catheter tubing, material characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. Angioplasty balloons and catheter tubing preferably have high strength for inflation at relatively high pressure, and high flexibility and softness for improved ability to track the tortuous anatomy. The balloon compliance, for example, is chosen so that the balloon will have a desired amount of expansion during inflation. Compliant balloons, for example balloons made from materials such as polyethylene, exhibit substantial stretching upon the application of tensile force. Noncompliant balloons, for example balloons made from materials such as PET, exhibit relatively little stretching during inflation, and therefore provide controlled radial growth in response to an increase in inflation pressure within the working pressure range. However, noncompliant balloons generally have relatively low flexibility and softness, making it more difficult to maneuver through various body lumens. Heretofore the art has lacked an optimum combination of strength, flexibility, and compliance, and particularly a low to non-compliant balloon with high flexibility and softness for enhanced trackability. Semi-compliant balloons made from semi-crystalline nylon 11, nylon 12, and copolymers of these nylons, such as poly ether block amide (for example, Pebax from Arkema) address these shortcomings and provide low distensibility and good flexibility, thus being used in many balloon dilatation catheters and stent delivery system.
For ease of thermal bonding to afore mentioned semi-compliant balloons, it is also preferred that the shaft of the balloon dilatation catheters and stent delivery system are also derived from same materials. Many balloon dilatation catheters and stent delivery systems therefore use shafts derived from these materials. The relative hardness and flexibility of the catheter tubing is also a constant compromise between the need for an agile tubing that can navigate the various body lumens, while having enough stiffness to be able to be pushed from a proximal end outside the body through the patient's vascular tract. A tubing that is relatively stiff will transmit proximal force more efficiently to the distal end, giving the practitioner more control over the location and position of the catheter balloon. However, stiffer tubing makes it much more difficult to bend or track curvatures in the body, leading to the paradox of the need for stiffer yet more flexible tubing. Moreover, stiffer materials when used to make catheter shafts have a higher tendency to kink, making it more difficult to control or push. Therefore, it is desirable to be able to increase stiffness and thus pushability by incorporating nylons having higher stiffness than semi-crystalline nylons having been used thus far. Some amorphous nylons offer desired higher stiffness than semi-crystalline nylons. However, the higher stiffness amorphous nylons are more susceptible to damage from solvents, such as isopropyl alcohol, used in the manufacturing, cleaning processes, and during clinical use. The present invention is directed to address this issue.